Registered reflective element for a brightness enhanced tir display

ABSTRACT

The brightness of a TIR-based display is enhanced with a registered reflective element by recycling and reflecting light that passes through the dark pupil region of each hemi-spherical protrusion in the hemi-spherical surface back to the viewer. A method to fabricate a brightness enhanced TIR display comprising an apertured membrane with a thin conductive reflective metal layer facing and registered with the pupils of the hemi-spherical surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/266,744, filed Apr. 30, 2014, which claims the filing date benefit ofProvisional Application 61/822,810 filed on May 13, 2013, the entiretyof which is incorporated herein by reference.

TECHNICAL FIELD

This application pertains to frustration of total internal reflection(TIR) in high brightness, wide viewing angle displays of the typedescribed in U.S. Pat. Nos. 6,885,496; 6,891,658; 7,286,280; 7,760,417and 8,040,591; all of which are incorporated herein by reference forbackground. More particularly, this application pertains to enhancingthe brightness in TIR-based displays.

BACKGROUND

FIG. 1 depicts a portion of a prior art reflective (i.e. front-lit)frustrated total internal reflection (TIR) modulated display 10 of thetype described in U.S. Pat. Nos. 6,885,496; 6,891,658; 7,760,417 and8,040,591. These patents describe an entirely new design of the outwardsheet that was previously described in U.S. Pat. Nos. 5,959,777;5,999,307; 6,064,784; 6,215,920; 6,304,365; 6,384,979; 6,437,921;6,452,734 and 6,574,025 which comprised of, for example, variousspatially uniform prism structures, dielectric light fibers, parallel,and perpendicular and interleaved structures. As a result of the closelypacked, spherical or hemi-spherical beaded, outward sheet design firstdescribed in patents ‘496’ and ‘658’, the practical angular viewingrange of frustrated TIR or other reflective display methods wasincreased. The new design offers semi-retro-reflective gain, wherebylight rays which are incident on the surface of the convex protrusionsin the shape of hemispherical beads are reflected back (but not exactlyretro-reflected) toward the light source; which means that thereflection is enhanced when the light source is overhead and slightlybehind the viewer, and that the reflected light has a diffusecharacteristic giving it a white appearance, which is desirable inreflective display applications.

Display 10 in FIG. 1 includes a transparent outward sheet 12 formed bypartially embedding a large plurality of high refractive index (e.g.η₁>˜1.90) transparent spherical or approximately spherical beads (it isnoted that said spherical or approximately spherical beads may also be“hemi-spherical beads” or “hemi-beads” or “beads” or “hemi-sphericalprotrusions” or “hemi-spheres” or “convex protrusions” and these termsmay be used interchangeably) 14 in the inward surface of a highrefractive index (e.g. η₂˜η₁) polymeric material 16 having a flatoutward viewing surface 17 which viewer V observes through an angularrange of viewing directions Y. The “inward” and “outward” directions areindicated by double-headed arrow Z. Beads 14 are packed closely togetherto form an inwardly projecting monolayer 18 having a thicknessapproximately equal to the diameter of one of beads 14. Ideally, eachone of beads 14 touches all of the beads immediately adjacent to thatone bead. Minimal interstitial gaps (ideally, no gaps) remain betweenadjacent beads.

An electro-active TIR-frustrating medium 20 is maintained adjacent theportions of beads 14 which protrude inwardly from material 16 bycontainment of medium 20 within a reservoir 22 defined by lower sheet24. An inert, low refractive index (i.e. less than about 1.35), lowviscosity, electrically insulating liquid such as, but not limited to,Fluorinert™ perfluorinated hydrocarbon liquid (η₃˜1.27) available from3M, St. Paul, Minn. is a suitable fluid for the medium 20. Other liquidssuch as Novec™ also available from 3M may also be used as the fluid formedium 20. A bead:liquid TIR interface is thus formed. Medium 20contains a finely dispersed suspension of light scattering and/orabsorptive particles 26 such as inorganic or organic pigments, dyes,dyed or otherwise scattering/absorptive silica or latex particles, etc.Sheet 24's optical characteristics are relatively unimportant as sheet24 need only form a reservoir for containment of electro-activeTIR-frustrating medium 20 and particles 26, and serve as a support forbackplane electrode 48.

In the absence of TIR-frustrating activity, as is illustrated to theright of dashed line 28 in FIG. 1, a substantial fraction of the lightrays passing through sheet 12 and beads 14 undergoes TIR at the inwardside of beads 14. For example, representative incident light rays 30 and32 are refracted through material 16 and beads 14. The light raysundergo TIR two or more times at the bead:liquid TIR interface, asindicated at points 34 and 36 in the case of ray 30; and indicated atpoints 38 and 40 in the case of ray 32. The totally internally reflectedrays are then reflected back through beads 14 and material 16 and emergeas rays 42 and 44 respectively, achieving a “white” appearance in eachreflection region or pixel.

A voltage can be applied across medium 20 via electrodes 46 and 48 whichcan for example be applied by, for example, vapor-deposition to theinwardly protruding surface portion of beads 14 and to the outwardsurface of sheet 24. Electrode 46 is transparent and substantially thinto minimize its interference with light rays at the bead:liquid TIRinterface. Backplane electrode 48 need not be transparent. IfTIR-frustrating medium 20 is activated by actuating voltage source 50 toapply a voltage between electrodes 46 and 48 as illustrated to the leftof dashed line 28, suspended particles 26 are electrophoretically movedinto the region where the evanescent wave is relatively intense (i.e.within about 0.25 micron of the inward surfaces of inwardly protrudingbeads 14, or closer). When electrophoretically moved as aforesaid,particles 26 scatter or absorb light, thus frustrating or modulating TIRby modifying the imaginary and possibly the real component of theeffective refractive index at the bead:liquid TIR interface. This isillustrated by light rays 52 and 54 which are scattered and/or absorbedas they strike particles 26 inside the thin evanescent wave region atthe bead:liquid TIR interface, as indicated at points 56 and 58respectively, thus achieving a “dark” appearance in each TIR-frustratednon-reflective absorption region or pixel. Particles 26 need only bemoved outside the thin evanescent wave region, by suitably actuatingvoltage source 50, in order to restore the TIR capability of thebead:liquid TIR interface and convert each “dark” non-reflectiveabsorption region or pixel to a “white” reflection region or pixel.

As described above, the net optical characteristics of outward sheet 12can be controlled by controlling the voltage applied across medium 20via electrodes 46 and 48. The electrodes can be segmented toelectrophoretically control the particles suspended in the TIRfrustrating, low refractive index medium 20 across separate regions orpixels of sheet 12, thus forming an image.

As shown in FIGS. 2A-2G of a closer examination of an individualhemi-bead 60, reflectance of a the hemi-bead 60 is maintained over abroad range of incidence angles, thus enhancing display 10's wideangular viewing characteristic and its apparent brightness. For example,FIG. 2A shows hemi-bead 60 as seen from perpendicular incidence—that is,from an incidence angle offset 0° from the perpendicular and r is theradius of the hemispherical bead. In this case, the portion 80 ofhemi-bead 60 appears as an annulus. The annulus is depicted as white,corresponding to the fact that this is the region of hemi-bead 60 whichreflects incident light rays by TIR, as aforesaid. The annulus surroundsa circular region 82 which is depicted as dark, also referred to as the“pupil”, corresponding to the fact that this is the non-reflectiveregion of hemi-bead 60 within which incident rays pass through and maybe absorbed and do not undergo TIR. FIGS. 2B-2G show hemi-bead 60 asseen from incident angles which are respectively offset 15°, 30°, 45°,60°, 75°, and 90° from the perpendicular. Comparison of FIGS. 2B-2G withFIG. 2A reveals that the observed area of reflective portion 80 ofhemi-bead 60 decreases only gradually as the incidence angle increases.Even at near glancing incidence angles (e.g. FIG. 2F) an observer willstill see a substantial part of reflective portion 80, thus givingdisplay 10 shown in FIG. 1 a wide angular viewing range over which highapparent brightness is maintained.

SUMMARY

The reflective, white annular region 80 surrounding the non-reflective,dark circular region 82 shown in FIGS. 2A-2G presents a problemsometimes referred to as the “dark pupil” problem which reduces thereflectance of the display. The display's performance is further reducedby transparent electrode 46, which may be formed by provision of atransparent conductive coating on hemi-beads 14 as shown in FIG. 1. Suchcoatings typically absorb about 5% to 10% of the incident light. Since aTIR light ray typically reflects several times, this can make itdifficult to achieve efficient reflection. The dark pupil problem can beaddressed by reflecting light rays back towards hemi-beads 14 (i.e.“recycling”) which pass through the non-reflective, dark circular regionof any of the plurality of hemi-beads 14 in display 10 in FIG. 1. Theinvention described in this application is directed to “recycling” ofsuch light rays to enhance the brightness in TIR-based displays.

An embodiment of the invention describes the addition of a reflectiveelement comprising of, for example, an apertured, insulating membranefacing the surface of convex protrusions in the shape of hemi-beads orhemi-spheres further comprising a conductive coating which additionallyavoids the need for a transparent conductive coating on thehemi-spherical surface. The membrane with a reflective and conductivelayer facing the inward hemi-bead/hemi-spherical surface issubstantially registered with the circular regions of the hemi-beadssuch that when light rays that pass through the dark pupil region of theoutward sheet comprising of a hemi-bead/hemi-spherical inward surfaceduring the light state of the TIR display are recycled and reflectedback to the viewer. A method to fabricate said registered and reflectivemembrane is additionally described herein.

The foregoing examples of the related art and limitations relatedthereto are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than restrictive.

FIG. 1 is a greatly enlarged, not to scale, fragmented cross-sectionalside elevation view, of a portion of a TIR frustrated or modulated priorart reflective image display.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F and 2G depict the hemi-bead or hemi-sphere,as seen from viewing angles which are offset 0°, 15°, 30°, 45°, 60°, 75°and 90° respectively from the perpendicular.

FIG. 3 depicts a TIR display in the light state (left of the dottedline) and dark state (right of the dotted line) with an unregisteredreflective membrane where light rays pass through the dark pupil regionsand are lost by escaping through the apertures.

FIG. 4 depicts a TIR display in the light state (left of the dottedline) and dark state (right of the dotted line) wherein a reflectiveelement comprising a membrane with a thin metal reflective andconductive coating is substantially registered (i.e. aligned) with thepupil of each hemi-sphere in the hemi-spherical inward surface such thatlight rays that pass through the pupils are reflected back through thepupils and back towards the viewer.

FIGS. 5A, 5B, 5C and 5D depict an idealized process to partiallyfabricate a display with a membrane with a thin metal conductivereflective coating aligned to the pupils of the hemi-sphericalprotrusions in the hemi-spherical inward surface.

FIGS. 6A, 6B and 6C depict the remaining process steps to fabricate adisplay with a membrane with a thin metal reflective and conductivecoating aligned to the pupils of the hemi-spherical protrusions in thehemi-spherical inward surface.

FIG. 7 is a top view of a portion of the patterned and etched porousmembrane with a reflective and conductive thin metal layer showing aplurality of apertures in an ordered array.

DETAILED DESCRIPTION

Throughout the following description specific details are set forth inorder to provide a more thorough understanding to persons skilled in theart. However, well known elements may not have been shown or describedin detail to avoid unnecessarily obscuring the disclosure. Accordingly,the description and drawings are to be regarded in an illustrative,rather than a restrictive, sense.

FIG. 3 depicts a cross-section of display 100 comprising of atransparent outer sheet 102 further comprising of a plurality ofinwardly protruding convex protrusions in the shape of hemi-spheres 104forming a contoured surface 106. As depicted, display 100'shemi-spherical surface 106 is formed integrally with display 100'stransparent outer sheet 102, whereas prior art display 10'shemi-spherical surface is formed by a closely packed layer of discretebeads 14 partially embedded in sheet 12. Either form or other similarhemi-spherical surface structure can be used. It should be notedforthwith that hemi-spherical protrusions may also be described moregenerally as convex protrusions and is covered by the inventiondescribed herein. It is not intended to limit the invention describedherein by using the term hemi-spherical protrusions or hemi-spheres, butsimply to be more descriptive of an optional shape of the convexprotrusions illustrated in the drawings.

Display 100 in FIG. 3 further comprises a thin electrically insulatingmembrane 108 placed between the hemi-spherical surface 106 and abackplane electrode 110. Membrane 108 may be formed of a polymericmaterial such as, but not limited to, Mylar® or polycarbonate, or someother material such as metal or glass. Membrane 108 further comprises athin metal layer 112 on the outward side of membrane 108 which faces thehemi-spherical surface 106 acting as both an electrode and a light rayreflector. Membrane 108 is a continuous (represented by dotted lines 114to imply a continuous layer) and apertured porous material. The metallayer 112 is also continuous (represented by dotted lines 116 to imply acontinuous layer) and apertured like the membrane 108 such thatapertures 118 penetrate both the metal layer and membrane 108. Display100 contains a low refractive index medium 120 maintained between andadjacent the hemi-spherical surface 106 and backplane electrode 110.Suspended within the medium 120 are light absorbing, electrophoreticallymobile particles 122 that can pass through apertures 118 in membrane108, as display 100's pixels are selectively switched between the lightreflecting TIR state depicted on the left side of the vertical dottedline in FIG. 3 and the dark or light absorbing frustrated TIR statedepicted on the right side of the vertical dotted line in FIG. 3.

In the light reflecting state showed to the left of the vertical dottedline in FIG. 3, particles 122 are attracted to and accumulate at thebackplane electrode 110. In the light absorbing or dark state as shownto the right of the vertical dotted line in FIG. 3, particles 122 areattracted to the metal layer 112 atop membrane 108 and adjacent thehemi-spherical surface 106 where TIR is frustrated thus preventing lightbeing reflected outwardly through the dark pupil region of thehemi-spherical protrusions or hemi-beads which form the hemi-sphericalsurface 106.

More particularly, in the light reflecting state, a substantial fractionof the light rays passing through the transparent outward sheet 102undergo total internal reflection (TIR) at the inward side of thehemi-spherical surface 106. For example, the incident light ray 124 isrefracted through sheet 102 and hemi-spherical surface 106. The rayundergoes TIR two or more times at the hemi-spherical:liquid TIRinterface as indicated (This is also depicted in FIG. 1 for display 10by light rays 30 and 32). The totally internally reflected ray is thenrefracted back through the hemi-spherical surface 106 and sheet 102 andemerges as ray 126 achieving a “white” appearance of display 100.

Other incident light rays, such as representative rays 128, are “lost”in the sense that they do not emerge outwardly from display 100. Forexample as depicted on the left side of the vertical dotted line in FIG.3, representative light rays 128 may instead pass through the apertures118 of membrane 108 and may be, for example, absorbed or redirected in anon-semi-retro-reflective manner at an inner wall portion of theaperture 118 or be absorbed by the particles 122 that are accumulated atthe backplane electrode 110.

A switchable voltage can be applied across the low refractive indexmedium 120 containing light absorbing electrophoretically mobileparticles 122 via electrodes 110 and 112. When a pixel of display 100 isswitched into the light absorbing or dark state as depicted to the rightof the dotted line in FIG. 3, particles 122 are electrophoreticallymoved through the apertures 118 of membrane 108 toward front electrode112. The particles form a relatively thick layer on electrode 112, suchthat particles make optical contact with the inward side of thehemi-spherical surface 106, thus frustrating TIR (i.e. particles 122 arewithin about 500 nm of the hemi-spherical surface 106, or closer). Theparticles 122 that have been moved electrophoretically adjacent thehemi-spherical surface 106 scatter or absorb light, by modifying theimaginary and possibly the real component of the effective refractiveindex at the hemi-spherical:liquid TIR interface. This is illustrated byrepresentative light rays 130 which are scattered and/or absorbed asthey strike particles 122 inside the evanescent wave region at thehemi-spherical:liquid TIR interface, thus achieving a “dark” appearancein each non-reflective absorption region or pixel (This is also furtherrepresented in display 10 in FIG. 1 by light rays 52 and 54).

The net optical characteristics of display 100 can be controlled by avoltage source 132 controlling the voltage applied across the lowrefractive index liquid 120 via electrodes 110 and 112. The electrodescan be segmented to control the electrophoretic movement of theparticles 122 suspended in liquid 120 across separate regions or pixelsof hemi-spherical surface 106, thus forming an image.

The reflectance of the membrane depends on both the degree of porosityand the intrinsic reflectance of the coating material. The selection ofporosity and intrinsic reflectance would depend, for example, on desiredspeed and overall desired reflectance as well as cost and materialimplications. The intrinsic reflectance of the coating material mayrange from about 75% to about 95%, and the porosity range from about 10%to about 50%. This means that the upper level of the reflectance may beabout 86% (0.95×0.90) and the lower level would be about 38% (0.75×0.5).In one exemplary embodiment, each hemisphere in the hemi-sphericalsurface 106 may have a diameter of at least about 2 microns. Membrane108 may be a flat sheet approximately 10 microns thick, perforated withabout 10 micron apertures 118 spaced on roughly 30 micron centers, suchthat the area fraction of apertures 118 in membrane 108 is at leastabout 10% and up to about 50%. Metal layer 112 may be formed on membrane108 by coating membrane 108's outward surface with a reflectiveconductive material such as a vacuum deposited thin metal film comprisedof, but not limited to, aluminum, gold or silver. Such an embodiment ofmembrane 108 is about 80% reflective (i.e. approximately 80% of thelight rays incident on membrane 108 do not encounter one of apertures118 and are reflected by metal layer 112).

Backplane 134 (which bears planar backplane electrode 110) may be aconventional thin film transistor (TFT) array. Appropriate relativespacing and alignment of transparent outward sheet 102, membrane 108 andrear electrode layer 110 can be achieved by providing spacer beadsand/or spacers (not shown).

In the reflective state shown on the left side of the vertical dottedline in FIG. 3, typically about half of the light rays incident on sheet102 are reflected by TIR. The remaining light rays reach membrane 108and 80% of those rays are reflected by metal layer 112 where a net totalreflectance of about 85% may be achieved. Furthermore, if membrane 108is positioned approximately at the focal plane of hemi-spherical surface106, metal layer 112 will retro-reflect light rays, achieving an opticalgain enhancement for all of the reflected light rays, and yielding aneffective reflectance of up to 200% in lighting environments where theprimary source of illumination directs light onto the outward surface ofoutward sheet 102 from overhead (i.e. from above the display viewer'shead) or somewhat from behind, rather than the primary source ofillumination being positioned in front of the viewer.

The apertured porous membrane 108 with the reflective electrode coating112 depicted in FIG. 3 is non-registered or non-aligned to the convexhemi-spherical protrusions of the hemi-spherical surface 106. Thisallows some of apertures 118 to be aligned or partially alignedimmediately below the pupil of each hemi-sphere. As a result, light raysthat pass through the transparent outward sheet 102 and through thehemi-spherical surface 106 are lost as they pass through the apertures118 and, for example, are absorbed or redirected in anon-semi-retro-reflective manner by the inner portion of an aperturewall or by the particles 122 accumulated at the backplane electrode 110or by particles 122 that may be suspended in the low refractive indexmedium 120. Ideally, in order to minimize the amount of light rays thatpass through the dark center or “pupil” of each hemi-sphere at thehemi-spherical surface 106 that are not recycled and are “lost” apreferred embodiment is to have the membrane 108 registered with thedark centers or pupils of each hemi-bead or hemi-spherical protrusionsuch that no apertures 118 are aligned or partially aligned below ahemi-bead or hemi-sphere pupil. Instead it is preferred to have eachpupil substantially aligned with a portion of membrane 108 that iscoated with the reflective electrode 112 such that light rays that passthrough the dark center or pupil of each hemi-bead or hemi-spherestrikes the reflective electrode 112 and are reflected back or recycledthrough the pupils of the hemi-spherical surface 106 and back to theviewer creating a second mode of reflectance. Another description ofthis invention is to have very low porosity regions of the membrane 108below the pupils to prevent light rays being lost in the display andhigh porosity elsewhere to allow for an unimpeded high rate of particle122 movement between electrodes 110 and 112.

FIG. 4 depicts a display 200 similar to display 100 except eachhemi-spherical dark center or pupil is no longer aligned with anaperture 118 directly below as shown in FIG. 3. Instead, in display 200in FIG. 4 each pupil within the plurality of hemi-spherical protrusions204 is substantially aligned with a portion of the continuous porousmembrane 208 (dotted lines 214 imply a continuous membrane layer) thatis coated with a continuous conductive reflective coating 212 (dottedlines 216 imply a continuous reflective layer) composed, for example, ametal. On the left side of the dotted line in display 200 is depictedthe light or TIR state where the particles 222 are accumulated at thebackplane electrode 210 by application of the appropriate voltage by avoltage source 232 across the low refractive index medium 220 withsuspended electrophoretically mobile particles 222. Light rays, such asrepresentative light ray 224, undergoes TIR and emerges asretro-reflected light ray 226. In display 100 in FIG. 3, light rays 128that are not totally internally reflected but instead pass through thedark center or pupil of the hemi-bead or hemi-sphere and subsequentlypass through apertures 118 aligned below the pupils of thehemi-spherical protrusions are not recycled and are lost by absorptionor redirected in a non-semi-retro-reflective manner by the inner wall ofthe apertures or by the particles 122 accumulated at the backplaneelectrode 110 or by some other means. In contrast in display 200 in FIG.4, membrane 208 with conductive reflective coating 212 is substantiallyaligned directly below the hemi-sphere pupils where incident light rays228 are instead returned as reflected light rays 229 by the conductivereflective coating 212 back through the dark centers or pupils of thehemi-spheres and back to the viewer resulting in recycling of the lightrays and an overall increase in reflectance and brightness of thedisplay as previously mentioned above.

On the right side of the dotted line in display 200 in FIG. 4 depictsthe frustrated TIR or dark state of the display. An electric field ofopposite polarity to that creating the light state on the left side ofthe dotted line is applied by voltage source 232 across the front 212and rear electrode 210 (rear electrode supported by backplane 234) toelectrophoretically move particles 222 through apertures 218 towards thefront electrode and within the evanescent region at the hemi-sphericalsurface 206 to frustrate TIR. Light rays 230 are thus absorbed as theypass through sheet 202 to the hemi-sphere:liquid TIR interface. The rearelectrode and backplane structure may be comprised of a TFT array.Additionally, display 200 (or display 100) may further comprise a colorfilter array situated on the outward surface of sheet 202 (or on outwardsurface of sheet 102) of red, green and blue or cyan, magenta and yellowsub-pixels. Display 200 may further comprise a front light.

Ideally, one method to improve the alignment of the reflective electrodecoated membrane 212 to the hemi-sphere pupils is to physically align orregister the porous apertured membrane 208 comprising of a top metallayer 212 with the hemi-sphere pupils such that the coated membrane 208is substantially directly below each hemi-sphere pupil as depicted indisplay 200 in FIG. 4. This may be difficult to assemble especially fora color display comprising of a color filter array where thehemi-spheres will likely need to be about 10 microns or less indiameter. Photolithography, also referred to as ultra-violet (UV)lithography or optical lithography, is a process to micro-fabricatepatterns of thin films of metals or other materials with precisedimensions as small as tens of nanometers and may be utilized to alignthe pupils with an apertured porous membrane. The following is anon-limiting example of a photolithographic process to fabricate analigned system as depicted in display 200 in FIG. 4. A uniform andcontinuous non-porous membrane 308 is coated on each side with a thinconductive reflective metal coating with metal layer 312 facing theinward hemi-spherical surface 306 and thin metal layer 319 facing thebackplane electrode surface 310 as shown in display 300 in FIG. 5A. Thinmetal coatings 312 and 319 may be the same composition of metal or maybe different metals. Metal coatings 312 and 319 additionally may be thesame or different thicknesses. For example, if the metal layer 319facing the backplane electrode 310 is present to protect membrane 308during the photolithographic process, it may only be necessary that thisrear metal layer 319 is much thinner than the top metal layer 312 toreduce the etch time and amount of etchant used to remove metal layer319. By metal layers 312 and 319 being of different composition,etchants may be chosen to selectively and sequentially remove the metallayers.

On top of thin metal coating 312 is coated a light-sensitive chemicalphotoresist 315. A variety of methods may be employed to coat thephotoresist 315 such as, but not limited to, spin coating or spraycoating. The metal-membrane-metal-photoresist layered structure319-308-312-315 is placed between the hemi-spherical inward surface 306and the backplane electrode 310 (with backplane support 334) such thatthe side of the structure with the photoresist top coat 315 directlyfaces the hemi-spherical surface 306 of the inward sheet 302 comprisingof the plurality of hemi-spheres 304 as shown in FIG. 5A.

The photoresist layer 315 is irradiated with a high intensity lightsource 321 such as near UV or UV light that is partially collimated andperpendicular to the photoresist later 315 through each hemi-sphere darkcenter or pupil. All other light not striking the pupil region will betotally internally reflected and not contribute to striking thephotoresist surface. The photoresist layer 315 undergoes a chemicalchange only where the light passes through the plurality of hemi-spherepupils and interacts with the photoresist layer 315 creating a patternedstructure. The photoresist layer 315 is then developed and rinsed with achemical solution (i.e. developer) such that the regions not exposed tothe high intensity light rays 321 are washed, rinsed or stripped awayand removed to leave a patterned photoresist layer 315 as shown in FIG.5B (Dotted lines 317 imply the photoresist layer is continuous). Thisprocess described herein is a negative photoresist process. A positivephotoresist process may also be used where the area stricken by the highintensity light rays are instead washed away.

The next step in an idealized process to create an aligned reflectivemembrane with the hemi-sphere pupils is to etch away the top metal layer312 that is exposed and not protected by the patterned photoresist layer315 as is shown in FIG. 5C. In this example, a selective etchant ischosen to only etch the top metal layer 312 and leave the bottom metallayer 319 unaffected. A portion of the still uniform and continuousmembrane 308 is exposed as shown in FIG. 5C. Another method that may beused if top and bottom metal layers 312 and 319, respectively, are ofthe same chemical composition is to use a thicker bottom metal layer 319than top metal layer 312. The etchant will remove top metal layer 312located adjacent the hemi-spherical surface 306 that is exposed and notcovered by the photoresist layer 315 first before the bottom metal layer319 is etched away. More particularly, if top metal layer 312, forexample, is 4 microns in thickness and bottom metal layer 319 is 8microns in thickness, etching both sides with the same chemical etchantfor the same amount of time at the same rate such that the top metallayer 312 is sufficiently etched away to remove a film of 4 microns,this would leave the bottom metal layer 319 thickness after etching ofabout 4 microns thick to be etched at a later time.

The exposed continuous membrane 308 is then etched with a second etchantto leave a continuous porous membrane 308 (represented by dotted lines314 to imply a continuous layer) with apertures 318 as shown in FIG. 5D.The etchant used to remove the exposed portions of membrane 308 andleave a porous membrane structure may selectively etch away only themembrane which is comprised of a material that may be etched with, forexample, an organic solvent or water.

The final etch step is to remove the thin bottom metal layer 319 shownin display 300 in FIG. 6A that faces the backplane electrode 310 leavinga structure found in FIG. 6B. The remaining photoresist layer 315 isstripped away using a chemical stripper that either dissolves thephotoresist and or alters the adhesion of the remaining photoresist 315to the patterned thin top metal layer 312 such that it can easily beremoved to form a display 300 that has an apertured membrane withapertures 318 comprising of a reflective conductive layer 312 alignedbelow each dark center or pupil of each hemi-sphere on the inward facinghemi-spherical surface 306 comprised of a plurality of hemi-spheres 304as shown in FIG. 6C.

The view of the etched membrane structure 308 with thin metal layer 312shown in FIG. 6C is a cross section. Dotted lines 314 imply that themembrane structure is a single continuous layer and dotted lines 316imply the metal layer is also continuous. A better view of the finaletched membrane:metal structure 308:312 is shown in FIG. 7. FIG. 7illustrates an overhead or top view of the etched membrane:metalstructure 308:312 looking onto the top metal layer 312 showing aplurality of apertures 318 in an idealized ordered array correspondingto the plurality of dark centers or pupils of the hemi-spheres withinthe hemi-spherical layer 304 of front sheet 302. Said membrane structurehas a thin conductive metal layer 312 on top of the membrane 308preferably facing the hemi-spherical surface 306.

The display 300 shown in FIG. 6C may be further filled with a lowrefractive index or other common refractive index liquid medium withsuspended light absorbing electrophoretically mobile particles as shownin display 200 in FIG. 4 along with additional performance enhancingadditives such as, but not limited to, viscosity modifiers and particlestabilizers. The display would be driven by a voltage source. Spacers orspacer beads may additionally be added. The display 300 shown in FIG. 6Cmay also alternatively be filled with a gas such as air or carbondioxide and electrophoretically mobile particles.

In the display embodiments described herein, they may be used inapplications such as in, but not limited to, electronic book readers,portable computers, tablet computers, wearables, cellular telephones,smart cards, signs, watches, shelf labels, flash drives and outdoorbillboards or outdoor signs.

While a number of exemplary aspects and embodiments have been discussedabove, those skilled in the art will recognize certain modifications,permutations, additions and sub-combinations thereof. The abovedescription of a frustratable TIR-based display with a substantiallyregistered and aligned reflective element to reflect light passingthrough the dark pupil regions and a process to fabricate saidfrustratable TIR display with an aligned conductive reflective porousmembrane to maximize the reflectance and brightness of the display andimprove the overall performance of said TIR display is intended to beconstrued in an illustrative and not limitative sense.

What is claimed is:
 1. A totally internally reflective display with abrightness enhancing structure, the display comprising: a transparentsheet comprising a plurality of transparent convex or hemi-sphericalprotrusions on the inward side of said sheet; a backplane electrode; anda reflective element substantially aligned or registered below the darkcenter or pupil of each said convex or hemi-spherical protrusion toprevent light rays passing through said pupils from not substantiallybeing recycled and reflected back to the display.
 2. The totallyinternally reflective display with a brightness enhancing structureaccording to claim 1, further comprising: a low refractive index mediumbetween the convex or hemi-spherical surface and backplane electrode; aplurality of light absorbing electrophoretically mobile particlessuspended in the low refractive index medium; and a voltage source forapplying a voltage across said low refractive index medium with saidsuspended light absorbing electrophoretically mobile particles, betweenthe light reflecting electrode and the backplane electrode.
 3. Thetotally internally reflective display with a brightness enhancingstructure according to claim 2, wherein the reflective element is anapertured membrane comprising a conductive reflective coating acting asa front electrode substantially aligned or registered below the darkcenter or pupil of each said convex or hemi-spherical protrusion toprevent light rays passing through said pupils from not substantiallybeing recycled and reflected back to the display.
 4. The totallyinternally reflective display with a brightness enhancing structureaccording to claim 3, wherein the voltage source is switchable to apply:a first voltage between the conductive light reflecting electrodealigned with the pupils of the convex or hemi-spherical protrusions onthe inward surface of the transparent sheet and the backplane electrode,to move substantially all of the particles inwardly through theapertured membrane toward the backplane electrode to allow for totalinternal reflectance of light rays at the convex or hemi-sphericalsurface; and a second voltage between the light reflecting electrode andthe backplane electrode, to move substantially all of the particlesoutwardly through the apertured membrane toward the aligned orregistered light reflecting electrode to frustrate total internalreflectance of light rays at the convex or hemi-spherical surface. 5.The totally internally reflective display with a brightness enhancingstructure according to claim 2, further comprising a color filter array.6. The totally internally reflective display with a brightness enhancingstructure according to claim 4, further comprising a color filter array.7. The totally internally reflective display with a brightness enhancingstructure according to claim 2, further comprising a front light.
 8. Thetotally internally reflective display with a brightness enhancingstructure according to claim 4, further comprising a front light.
 9. Thetotally internally reflective display with a brightness enhancingstructure according to claim 6, further comprising a front light. 10.The totally internally reflective display with a brightness enhancingstructure according to claim 3 wherein the conductive reflectiveapertured membrane is substantially aligned with the pupils of theconvex or hemi-spherical protrusions of the transparent sheet isfabricated by a photolithographic process.
 11. A photolithographicprocess according to claim 10 comprising a combination of at least oneor all of the following sub-processes: coating a photoresist layer atopthe metal layer of the membrane facing the hemispherical surface;irradiating the photoresist layer with collimated high intensity lightthrough the pupils of the hemi-spherical protrusions; developing thephotoresist layer to leave a desired geometric pattern using a positiveor negative resist method; etching and removing the exposed unneededmetal layer; etching the membrane to form apertures; etching theprotective metal layer on the membrane facing the backplane electrode;and stripping the remaining photoresist.